This application claims the priority of German Application No. 19831249.0, filed Jul. 11, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and to a regulating and control unit for influencing the driving dynamics of a motor vehicle.
Printed publication DE-Z: ATZ 96 (1994) 11, pages 657 ff. gives a description of an electronic driving-dynamics regulating system by means of which active interventions into individual vehicle components are performed to improve dynamic driving behaviour. To provide input signals for the regulating system, the vehicle speed and the transverse acceleration are measured and are used together with further input variables, such as the steering-wheel angle, to determine a desired curve for the yaw rate. The deviation of the actual driving behaviour from the desired driving behaviour is determined by means of a comparison with the current actual yaw rate and used to determine a regulating intervention. As oversteer begins, the driving torque is reduced, for example, in order to increase the cornering potential of the wheels of the driven axle.
Another driving-dynamics regulating system is known from EP 05 54 892 A1. This printed publication discloses a system for traction control in motor vehicles with automatic transmission, using the shift state of the transmission and the vehicle speed as input signals and producing from these an actuating signal for adjusting the throttle-valve position to enable the driving torque to be adjusted.
German printed publication DE 35 45 716 A1, discloses a device for propulsion regulation on motor vehicles of which the intention is to prevents spinning of the driven vehicle wheels in cases where the slip of a wheel exceeds a threshold value. Additional conditions taken into account are the vehicle speed and the transverse acceleration, which are each checked to determine whether they exceed a limiting value. In this case, a limiting regulating intervention is performed on the throttle valve.
German Publication DE 36 12 170 A1 has furthermore disclosed using the change in the transverse acceleration over time as a control signal for reducing the output torque of the drive unit of a vehicle. Here, an actuator designed as an electronic engine output controller is activated to reduce the driving power.
German printed publication DE 37 41 009 A1 discloses a control apparatus for distributing the driving power of a vehicle with all-wheel drive, by means of a transmission clutch which can continuously vary a torque transmitted to the front axle. As the difference in wheel speed increases, there is an increase in the torque transmitted to the front axle with a steep rate of rise if the transverse acceleration is low and with a low rate of rise if the transverse acceleration is high. However, this control apparatus is intended exclusively for distributing driving torque between a front axle and a rear axle and cannot be used for vehicles with two-wheel drive.
One object of the invention is to provide a driving-dynamics system which provides additional adjustment facilities for influencing the driving dynamics of a motor vehicle.
Another object of the invention is to increase the stability of the vehicle.
Still another object of the invention is to provide a driving-dynamics system which is designed to be as simple a design as possible, and to use existing resources as far as possible.
These and other objects and advantages are achieved by the control method and apparatus according to the present invention, in which the vehicle""s longitudinal speed and the transverse acceleration are sensed and used to determine an actuating signal for the throttle-valve position and for the clutch. If either of the vehicle speed or the transverse acceleration exceeds a limiting value, the maximum opening angle of the throttle valve is limited, thereby also limiting the engine output. A maximum vehicle speed will then also be established, at least with given constant external circumstances. The method according to the invention has the advantage that, below the limiting value for the vehicle speed and/or the transverse acceleration, the throttle-valve position is determined solely by the demand made by the driver; whereas, above the limiting value, it is limited to a maximum opening angle. The output torque at the driven axle is thereby limited or reduced, if appropriate to the maximum drag torque of the engine. Limiting or reducing the driving torque means that the longitudinal forces acting on the driven vehicle wheels are smaller and the vehicle wheels are thus able to accept higher cornering forces, thereby increasing the stability of the vehicle.
This strategy exploits the system characteristics of a motor vehicle based on a drive-by-wire concept. Compared with known regulation concepts, the only additional hardware component is a sensor for measuring transverse acceleration no further vehicle components are necessary. The gain in stability is achieved with minimal additional expenditure on hardware.
Another advantage is that wheel braking is, initially, not necessary, thus eliminating the need to transmit via the wheels any additional longitudinal forces, which would limit the transmission of additional, stabilizing cornering forces.
As a further stabilizing intervention, the clutch discs can be separated, thus interrupting torque transmission in the drive line and freeing the driven axle or driven wheels completely from as driving torques and hence from longitudinal forces, thereby allowing maximum cornering forces to be transmitted.
Torque transmission is generally interrupted in extreme driving situations, which occur when the transverse acceleration has a steep gradient or a large change over time. The change in the transverse acceleration over time is compared with a limiting value; if the change in the transverse acceleration exceeds the limiting value, the clutch is opened.